1. Field of the Invention
The present invention relates to a lubricating structure for an internal combustion engine. More particularly, the present invention relates to a lubricating structure for an internal combustion engine in which a cam housing supporting a camshaft is provided on an upper portion of a cylinder head.
2. Description of the Related Art
Internal combustion engines for motorcycles and automobiles generally have a lubricating structure. Such a lubricating structure pumps up by an oil pump a lubricating oil stored in an oil pan provided on a lower surface of a crankcase and supplies the lubricating oil to parts such as a crankshaft in the crankcase, a piston in a cylinder, and a valve driving device in a cylinder head.
As a conventional lubricating structure for an internal combustion engine of this type, there has been publicly known, for example, one which supplies a lubricating oil drawn up by an oil pump to a piston in a cylinder, a valve driving device in a cylinder head, and so on via an oil passage formed in the cylinder head (see Patent Document 1, for instance).
[Patent Document 1] Japanese Utility Model Application Laid-open No. 03-6006
However, in the above-described conventional lubricating structure for the internal combustion engine, the oil passage is formed in the cylinder head. Such a structure imposes a layout restriction on a route, an inside diameter, and so on of the oil passage. Therefore, the oil passage is liable to become excessively long and thin. This has problems of difficulty in reducing resistance when the lubricating oil flows through the oil passage and inability to supply the lubricating oil efficiently to each part.